Method of installing an in-line structure in a pipeline

ABSTRACT

A method of installing an In-Line Structure (ILS) to a fluid-filled pipeline extending from a reel, over an aligner, and through a lay-tower during offshore reeling, the pipeline having an oblique part from the reel to the aligner, and a vertical part from the aligner through the lay-tower, including at least the steps of: (a) draining fluid in the fluid-filled pipeline from the vertical part of the pipeline to create a drained portion of the vertical part of the pipeline up to and around the aligner; (b) cutting the pipeline at or near the draining of step (a) to create upper and lower open ends of the pipeline; (c) installing the In-Line Structure to at least the upper open end of the pipeline; (d) locating a vent hose through a vent port in the In-Line Structure; (e) adding fluid into the drained portion of the pipeline and venting air from the drained portion of the pipeline through the vent hose to wholly or substantially fill the drained portion of the pipeline with the fluid.

The present invention generally relates to methods of installing anIn-Line Structure in a fluid-filled pipeline extending over a reel on avessel during offshore reeling, particularly but not exclusively apipeline having an internal liner. In particular, the methods can bepart of averting the wrinkling of an internal liner of the pipeline dueto bending during offshore reeling. The invention finds particularutility in the laying of Mechanically Lined (rigid steel) Pipeline (MLP)from a pipelaying vessel.

BACKGROUND TO THE INVENTION

In the reel-lay method of laying an offshore pipeline, the pipeline isprovided from a reel or spool on a vessel, towards a lay-tower designedto direct the pipeline down through the lay-tower and through a moonpoolin the vessel and into the sea for laying. The lay-tower may be in a‘vertical’ position relative to the general plane of the vessel, or atan angle thereto, generally by rotation of the lay-tower at or near apoint on the vessel.

At the top of the lay-tower is a circular aligner, typically a largegrooved wheel. Thus, the pipeline extends from the reel to the top ofthe tower in an ‘oblique’ direction compared to the ship level and thelay-tower, over the lay-tower aligner, and down through the lay tower.For the purposes of the present invention, the portion of the pipelineextending from the aligner and down through the lay-tower shall bedefined as a ‘vertical’ part of the pipeline, independent of the angleof the lay-tower relative to the vessel.

During offshore installation, there may be a requirement to install intothe pipeline a device or apparatus, for example an In-Line-Tee (or ILTor ‘T-piece’), a manifold, a PipeLine End Termination (PLET) also knownas FlowLine End Termination (FLET), or an Abandonment and Recovery Head(‘A&R’ Head) to perform an abandonment and recovery ‘A&R’ operation bythe addition of the Abandonment and Recovery Head (‘A&R’ Head) at theend of the pipeline known in the art. For the purposes of the presentinvention, any such apparatus, pipe, etc. to be installed ‘in-line’shall be defined as an In-Line Structure or ILS.

For the installation of such an In-Line Structure (ILS), the unreelingof the pipeline has to be interrupted, the pipeline cut in two parts,adjustment of the space between the cut ends optionally made to matchthe space required for the In-Line Structure (ILS), the In-LineStructure (ILS) installed between the pipeline's cut ends, before theunreeling of the pipeline can start again.

Where the pipeline is relatively thin or single layered, the change ofdirection of the pipeline from its oblique part to its vertical partaround the lay-tower aligner should not cause any significant damage tothe pipeline during laying, such that any movement of the pipelinerequired to create the space to insert the In-Line Structure (ILS), andthe re-start of reel-laying thereafter, is immediately possible. Such anarrangement is shown in for example U.S. Pat. No. 6,733,208, orWO2006/085739A.

However, there are some pipelines where it is desired to have themflooded and typically pressurised during reel-laying to minimise oravoid damage to the pipeline as it changes direction of the pipelinefrom its oblique part to its vertical part around the lay-tower aligner.The flooding and typical pressurisation of the pipeline with a fluidsuch as water or MEG, maintains an internal pressure within the pipelinein a manner known in art.

Such pipelines include Mechanically Lined Pipelines (MLP). Pipelines foruse in the subsea conveying of fluids such as gas or crude oil are oftenexposed to the corrosive effects of these fluids which, unless thepipeline is protected by some material resistant to their effect orcorrosion, can cause damage to the pipeline and even pipeline failure,which is difficult and expensive to remedy. Corrosion Resistant Alloys(CRA), such as Inconel™ 625, are known to provide resistance tocorrosion in extreme environments such as in oil and gas pipelines. Toavoid having to unnecessarily provide the entirety of the pipeline asrelatively high cost Corrosion Resistant Alloy (CRA), it is known toprovide bimetallic pipeline in which an outer, typically carbon steelpipeline is provided as a host pipe, the inner surface of which isprotected by a layer of a Corrosion Resistant Alloy (CRA).

It is known to provide bimetallic pipeline by cladding the inner surfaceof the carbon steel pipeline with a metallurgically bonded CorrosionResistant Alloy (CRA) layer, or even a weld overlay. However analternative method, which has in some cases a cost benefit, of producingbimetallic pipeline is to add a liner to the inner surface of the carbonsteel pipeline made from Corrosion Resistant Alloy (CRA) or othermaterial. The lining process involves the creation of a mechanical bondbetween the liner and the pipeline by inserting the liner into a lengthof the pipeline and hydraulically or mechanically expanding the pipelineand liner together, such that the liner undergoes a plastic deformationwhile the outer pipeline undergoes an elastic or plastic deformation.Upon relaxation of the expansion force or pressure, an interferencecontact stress or interference fit is produced at the interface betweenthe liner and the pipe, causing the liner to become mechanically bondedto the internal surface of the pipe.

While a Mechanically Lined Pipeline (MLP) may be preferable from apipeline manufacturing and cost-effectiveness perspective, a knownproblem is that, in pipeline construction methodologies that involvereeling the pipeline onto and off a storage spool during production andlaying, forces imparted on the pipeline during the reeling process bybending of the pipeline can cause the internal liner to wrinkle. Inreeling a Mechanically Lined Pipeline (MLP), significant bending strainis imparted to the pipeline as it is wound onto and unwound from astorage reel which can result in a significant amount of wrinkling inthe Corrosion Resistant Alloy (CRA) liner. The wrinkling mechanism maybe as a result of, among other things, the bending stress itself,ovalisation of the pipeline cross section, or differential longitudinalcompression and strains on the liner along the curvature of the bend dueto the periodic circumferential fixation of the liner in the region ofthe joining welds. This wrinkling is an undesirable result, as thewrinkles can cause mechanical and material issues with the liner (suchas embrittlement), as well as causing significant problems within thepipeline during and after the pipeline is commissioned and is in use,which can lead to the failure of the pipeline before the end of itsserviceable term.

To avoid wrinkling a reeled Mechanically Lined Pipeline (MLP), it isknown that a sufficiently thick Corrosion Resistant Alloy (CRA) or otherliner can reduce the likelihood or magnitude of wrinkling, or avoidwrinkling completely, when the pipeline is bent or deformed duringlaying. Indeed, due to this phenomenon, Corrosion Resistant Alloy (CRA)or lined pipeline is generally chosen for a specific project having aliner thickness sufficient to avoid wrinkling due to the laying process.In the case of corrosion resistant liners, the fundamental thickness ofthe Corrosion Resistant Alloy (CRA) liner that is required is that whichis sufficient to protect against corrosion over the serviceable life ofthe pipeline, and is dependent on the conditions in which the pipelineis to operate. In many cases the liner thickness that is used is greaterthan that needed to withstand chemical attack over the serviceable lifeof the pipeline, or that needed to successfully perform the function ofthe liner. For example, in the context of reeling a Mechanically LinedPipeline (MLP) onto and off of a spool, WO 2011/048430A discloses twomethodologies for calculating a minimum liner thickness necessary toavert wrinkling during reeling of a Mechanically Lined Pipeline (MLP).

Given that the cost per unit weight of Corrosion Resistant Alloy (CRA)and other liner materials can be very high, the cost of the linermaterial can become a significant component of the fixed material costsof the pipeline. Thus while using a sufficiently thick liner can reducewrinkling, it can also lead to the use of a large amount of an expensiveliner material. Where a thicker liner than is necessary to avoidcorrosion is still used to reduce wrinkling, the amount of linermaterial used can be far in excess of that needed for the pipeline tofunction properly and, e.g. to protect against chemical attack duringuse.

Other possible solutions to avoid wrinkling a reeled Mechanically LinedPipeline (MLP) during reel-laying are described in WO2008/072970A,WO2011/124919A, WO2011/051221A, WO2011/051218, and WO2010/010390. Theseinclude pressurising the entire length of the pipeline as it is reeledonto a storage reel, and later pressurising the entire length of thepipeline as it is unwound from the storage reel, straightened and laid,after which it is depressurised. The pressurisation appears to helpprevent the liner from wrinkling due to bending stresses in the pipelineon reeling and unreeling.

Where a pipeline is flooded and pressurised, there is also a need toensure the safety of the operators while the pipeline is cut and toguarantee the pressurisation of the pipeline during any movement of thepipeline, as well as when the unreeling starts again.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided amethod of installing an In-Line Structure (ILS) to a fluid-filledpipeline extending from a reel, over an aligner, and through a lay-towerduring offshore reeling, the pipeline having an oblique part from thereel to the aligner, and a vertical part from the aligner through thelay-tower, comprising at least the steps of:

(a) draining fluid in the fluid-filled pipeline from the vertical partof the pipeline to create a drained portion of the vertical part of thepipeline up to and around the aligner;

(b) cutting the pipeline at or near the draining of step (a) to createupper and lower open ends of the pipeline;

(c) installing the In-Line Structure to at least the upper open end ofthe pipeline;

(d) locating a vent hose through a vent port in the In-Line Structure;

(e) adding fluid into the drained portion of the pipeline and ventingair from the drained portion of the pipeline through the vent hose towholly or substantially fill the drained portion of the pipeline withthe fluid.

Optionally, the method comprises installing the In-Line Structure (ILS)between both the upper and the lower open ends of the pipeline. In thisway, after step (f), the offshore reeling of the re-joined pipeline fromthe vessel can continue.

In an alternative arrangement, the method further comprises the step ofinstalling a second In-Line Structure (ILS) to the lower open end of thepipeline. In this way, the laying of the lower part of the cut pipelinecan continue, and the offshore reeling of the upper part of the cutpipeline can continue, optionally at the same or a different time and/orlocation of the laying of the lower part of the cut pipeline.

Optionally, the flooding fluid in the fluid-filled pipeline ispressurised, and the method further comprises the step of relieving thepressure of the flooding fluid prior to step (a). Further optionally,the flooding fluid in the fluid-filled pipeline is re-pressurised afterstep (e).

Optionally, the method further comprises forming a hole in the verticalpart of the pipeline to allow the draining of the flooding fluid fromthe vertical part of the pipeline.

Optionally, the method further comprises wholly or substantiallyremoving the vent hose from the pipeline after step (e) and sealing thevent port in the In-Line

Structure.

Optionally, the method further comprises adding the flooding fluid instep (e) into the In-Line Structure.

Alternatively optionally, the method further comprises adding theflooding fluid in step (e) into the flooding fluid-filled oblique partof the pipeline.

Optionally, the method further comprises moving the oblique part of thepipeline between step (b) and step (c).

According to another aspect of the present invention, there is providedan apparatus for installing an In-Line Structure (ILS) to a floodingfluid-filled pipeline, extendable from a reel, over an aligner, andthrough a lay-tower during offshore reeling, the pipeline having anoblique part from the reel to the aligner, and a vertical part from thealigner through the lay-tower the apparatus comprising:

(a) a drain to drain flooding fluid from the vertical part of thepipeline to create a drained portion of the vertical part of thepipeline up to and around the aligner;

(b) a cutter to cut the pipeline at or near the draining of step (a) tocreate upper and lower open ends of the pipeline;

(c) an In-Line Structure having a vent port to install to at least theupper open end of the pipeline;

(d) a vent hose to be installed in the vent port of the In-LineStructure;

(e) flooding fluid to wholly or substantially refill the drained portionof the pipeline;

(f) a seal to seal the vent port after step (e).

DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdetailed description together with the appended illustrative drawings inwhich:

FIG. 1 is a schematic side view of a pipeline extending from a reel,over an aligner, and through a lay-tower during offshore reeling on avessel;

FIG. 2 is schematic cross-sectional view of a portion of a floodedpipeline being installed over an aligner and through a moonpool, showingprimary steps of a first embodiment of the present invention;

FIG. 3 shows further steps in embodiments of the present invention;

FIGS. 4 and 5 shows further steps in one embodiment method from FIG. 3on a part of the pipeline in FIG. 3 from its upper open end to thebeginning of its oblique part, without the aligner;

FIG. 6 shows the pipeline of FIGS. 2 and 3 with an installed and floodedIn-Line Structure; and

FIGS. 7 and 8 show further steps from FIG. 3 of another embodiment ofthe present invention.

DETAILED DESCRIPTION

Various examples and aspects of the invention will now be described indetail with reference to the accompanying figures. Still other aspects,features, and advantages of the present invention are readily apparentfrom the entire description thereof, including the figures, whichillustrates a number of exemplary embodiments and aspects andimplementations. The invention is also capable of other and differentexamples and aspects, and its several details can be modified in variousrespects, all without departing from the spirit and scope of the presentinvention. Accordingly, the drawings and descriptions are to be regardedas illustrative in nature, and not as restrictive. Furthermore, theterminology and phraseology used herein is solely used for descriptivepurposes and should not be construed as limiting in scope. Language suchas “including,” “comprising,” “having,” “containing,” or “involving,”and variations thereof, is intended to be broad and encompass thesubject matter listed thereafter, equivalents, and additional subjectmatter not recited, and is not intended to exclude other additives,components, integers or steps. Likewise, the term “comprising” isconsidered synonymous with the terms “including” or “containing” forapplicable legal purposes.

In this disclosure, whenever a composition, an element or a group ofelements is preceded with the transitional phrase “comprising”, it isunderstood that we also contemplate the same composition, element orgroup of elements with transitional phrases “consisting essentially of”,“consisting”, “selected from the group of consisting of”, “including”,or “is” preceding the recitation of the composition, element or group ofelements and vice versa.

FIG. 1 shows a method of reel-laying a pipeline 20 from a reel 4 on avessel 6 in the sea 8. In this method, the pipeline 20 is extended fromthe reel 4 over an aligner or aligner wheel 22 at or near the top of alay-tower 12. Thus, the part of the pipeline 20 being laid has an‘oblique part’ extending from the reel 4 up to the aligner 10, and a‘vertical part’ from the aligner 22 down through the lay-tower 12, (andsubsequently through a moonpool 14 or over the side or back of thevessel, and into the sea 8, generally for laying on a seabed (notshown)). This method of reel-laying is commonly faster and more economicthan the ‘stove-pipe’ method of laying, also known as J-lay method, andis therefore preferred where possible. The lay-tower 12 can be rotatedto be at a non-vertical angle relative to the vessel 6 in a manner knownin the art.

Where the pipeline 20 is relatively flexible, typically small diameter,and would not be affected or misshapen during its change in directionover the aligner 22 and straightening into the vertical pathway of thelay-tower 12, the installation of an In-Line Structure (ILS) 16(including but not shown an A&R pipe) during laying should only requirethe clamping of the pipeline 20 in the lay-tower 12 by one or moresuitable clamps (not shown), cutting of the pipeline, possibly a smallreverse movement of the pipeline back onto the reel to allow sufficientspace for insertion of the In-Line Structure (ILS) at the cut, joiningof the In-Line Structure (ILS) into the pipeline, and continuation ofthe reel-laying process.

It is desired to extend the usefulness of reel-laying to furtherpipelines, including those of increasing outer diameter such as >6inches (>15 cm), including for example pipeline diameters of 8 inches to18 inches (20.3 cm to 45.7 cm), and optionally with a liner, includingthin wall liners in the range 1-5 mm.

A particular form of bi-metallic pipeline has a main metal tube as arelatively thick outer pipe, typically formed from steel such as carbonsteel, and an internal liner having a thickness typically in the range2.5-3 mm, which is hydraulically or mechanically expanded within theouter pipe to form a Mechanically Lined Pipeline (MLP).

The main metal tube may be any length, including typical stalk lengthsof either 12 m, 24 m, 48 m, or possibly longer. The main metal tube maybe any internal diameter from 10 cm to 50 cm or greater. The main metaltube may be any thickness from 5 mm to 50 mm or greater. The main metaltube may be formed by extrusion. The main metal tube may be formed frommetal ingots which are pierced, for example by broaching, elongated andcalibrated, for example by rolling. The main metal tube may be formedfrom sheet bended generally with U-shape break press then O-shape breakpress, eventually expanded with an expander, and longitudinally seamwelded. The main metal tube may be formed from the assembly of a seriesof main metal tube stalk butt welded together.

The internal liner aims to provide an effective corrosion-resistantbarrier to the internal surface of the pipeline even in an aggressivesingle, dual and multiphase hydrocarbon environment at temperatures upto 130° C. and at high operating pressures. The liner may be formed of ametal, especially a Corrosion Resistant Alloy (CRA) such as an alloy316L, Super 13 Cr, 22 Cr duplex, 25 Cr duplex, Alloy 28, Alloy 825,Alloy 2550, Alloy 625, Alloy C-276, or any other suitable corrosionresistant alloy. The thickness of the metallic liner can be in the range0.5 mm to 3 mm, typically in the range 2.5-3 mm.

For the purpose of expanding the liner within the outer pipe, the linercan be pressurised from the inside, for example by injecting with a pumpa pressurized fluid such as water or oil, so as to expand the linercircumferentially to form interference contact stress between the linerand the main metal tube. Generally during the expansion, the linerundergoes a plastic deformation while the main metal tube undergoeseither an elastic or a plastic deformation, depending on themanufacturing process. One example of this comprises inserting the linerinside the main metal tube, and expanding the liner radially so that itcomes into contact with the main metal tube, and then the main metaltube outer diameter will also expand together with the liner to apre-determined strain level such that, following relaxation of theinternal pressure, an interference contact stress between the liner andthe main metal tube remains. Such a rigid pipe is generally known as aMechanically Lined Pipe (MLP).

It is increasingly desired to extend the usefulness of reel-laying toMechanically Lined Pipeline (MLP) pipelines.

To avoid wrinkling a reeled Mechanically Lined Pipeline (MLP) as it isstraightened from its reel position to a laying position, flooding theMechanically Lined Pipeline (MLP) with a suitable flooding fluid such aswater or MEG, and typically pressurising the flooding fluid, isbeneficial. This is discussed in more detail in for exampleWO2008/072970A, WO2011/124919A, WO2011/051221A, WO2011/051218, andWO2010/010390A. Typically, the entire Mechanically Lined Pipeline (MLP)pipeline is flooded and pressurised during the reel-laying process.

However, during offshore installation, there may be a requirement toinstall into the pipeline a device or apparatus, for example anIn-Line-Tee (or ILT or ‘T-piece’), a manifold, a PipeLine EndTermination (PLET) also known as FlowLine End Termination (FLET), or anAbandonment and Recovery Head (‘A&R’ Head) to perform an abandonment andrecovery ‘A&R’ operation by the addition of the Abandonment and RecoveryHead (‘A&R’ Head) at the end of the pipeline known in the art. For thepurposes of the present invention, any such apparatus, pipe, etc. to beinstalled ‘in-line’ shall be defined as an In-Line Structure or an ILS.

To install an In-Line Structure (ILS) involves completely cuttingthrough or across the pipeline at least once (once each side or part isheld by suitable clamps in the lay-tower), which will relieve theflooding (and any pressurisation) within the pipeline. But re-flooding(and usually re-pressurisation) of the part of the pipeline around thealigner is then required to continue the reel-laying operation. It ispossible to relieve the flooding of the whole length of the pipeline,but this then requires the burden of the re-flooding and usuallyre-pressurisation of the whole length of the pipeline, or at least thatpart of the pipeline still on the reel, which is an extensive exercisecausing a significant delay to the laying operation.

FIG. 2 shows part of the flooded pipeline 20 extending from the reel 4on the vessel 6 during offshore reel-laying, such that there is anoblique part 24 extending from the reel to the aligner 22, and arelative ‘vertical’ part 26 (optionally not being vertical) as itextends from the aligner 22 down through a lay-tower (not shown toassist clarity) and through a moonpool 28 in part of a vessel 30.

The pipeline 20 may be a Mechanically Lined Pipeline (MLP) as describedherein or a variant, and is not shown in further detail. During thereel-laying, the pipeline 20 is flooded with a flooding fluid 32 such aswater to reduce and/or avoid any internal damage and/or ovalisation tothe pipeline as it traverses from its oblique part 24 to its verticalpart 26 around the aligner 22 (and any other straighteners known in theart, and not shown herewith). Optionally, the flooding fluid 32 is alsopressurised, to enhance the mechanical effect of the fluid against suchdamage, possibly up to 3 MPa or more. Flooding of the pipeline can beachieved by a suitable entry port into the pipeline 20 at, in or nearthe reel, and using a suitable pump for any pressurisation desired.Generally there is an end cap or plug etc. at the other end of thepipeline 20.

In a first step of an embodiment of the method of the present inventionfor installing an In-Line Structure into the fluid-filled pipeline 20,fluid is drained from the vertical part 26 of the pipeline 20. This canbe achieved by forming an aperture in the pipeline 20 (once each side orpart is held by one or more clamps on the lay-tower 12) at a suitableposition such as at arrow A. The aperture could be formed by using a hotstab to form a hole in the pipeline 20, or opening a suitable locatedvent or other port in the pipeline 20.

Where the flooding fluid 32 is pressurised in the pipeline 20, thepressure could be relieved before making such an aperture, typically atthe fluid access point at or near the reel, such that the flooding fluid32 is then at a lower pressure before draining.

Referring to FIG. 3 the hole at arrow A leads to draining the floodingfluid 32 by gravity from the vertical part 26 of the pipeline 20 as perarrow B to create a drained portion 34 in the vertical portion 26 of thepipeline between the hole and up to the aligner 22. The drainingcontinues until the drainage reaches a ‘highest point’ at the apex ofthe pipeline 20 around the aligner 22. Thus, flooding fluid 32 remainsin the oblique part 24 of the pipeline.

Once the flooding fluid 32 is drained, the clamped pipeline 20 can becut to create separate upper and lower pipelines (each to be held by aseparate clamp of the lay-tower) to allow the installation of at leastone ILS at any suitable position. Cutting through a pipeline can becarried out by any suitable process and apparatus. A grinder, an orbitalcutter, or any other suitable cutting apparatus could be used. Thecutting creates an upper open end 36 of the upper or reel-end part ofthe pipeline, and a lower open end 38 of the lower part 33 of thepipeline extending into the sea 8.

There are many types, shapes and design of suitable ILSs forinstallation by the present invention, although most ILSs have a lengthin the range 1 to 12 m. FIG. 3 shows a representative ILS 37 to beinstalled. For a small or smaller length ILS, it is known that a small,minor or de minimus amount (generally being less than 1 m, andpreferably less than 0.7 m) of movement of the vertical part 26 of thepipeline 20 is possible in the direction of arrow C, i.e. back onto thereel, without any fluid therein, if required to provide sufficient spacebetween the upper open end 36 and the lower open end 38 of the pipeline20 to fit the In-Line Structure (ILS) 40 at this stage if desired. Thus,only one cut of the pipeline is necessary.

For larger/longer ILSs, a second cut, for example at arrow D, can becarried out to remove a section of the pipeline 20 and create the spacerequired to fit the longer In-Line Structure (ILS) between the loweropen end 38 and a new upper end (not shown) of the pipeline 20.

It may be desired by the operator to make more than one or two cuts forother reasons, and this does not affect the present invention. The firstcut and any second etc. cut is typically at or either side of thedrilled hole at arrow A.

In an alternative to a second cut, an end cap, typically having a body,one or more sealing elements such as an O-ring of inflatable packer ofblade, a pipeline fixation means and a suitable pressurising means andaperture therethrough (not shown), could be added to the upper open end36 to allow pressurisation of the air in the drained portion 34, (or toallow the injection of another suitable gas or liquid) that providessufficient internal pressure to allow a greater (than a small, minor orde minimus) amount of movement of the vertical part 26 of the pipeline20 back over the aligner 22, to provide the required space between theupper open end 36 and the lower open end 38 of the pipeline 20 to fitthe In-Line Structure (ILS) at this stage if desired.

For clarity, FIGS. 4 and 5 show a foreshortened view of the portion ofthe pipeline 20 between an In-Line Structure and the beginning of theoblique part 24 with fluid 32 therein, also without the aligner 22.

In a first particular embodiment of the present invention, FIG. 4 showsthe installation such as by welding of a first In-Line Structure (ILS)such as an In-Line T-piece (ILT) 40 to the previously upper open end 36of the upper part of the pipeline 20. FIG. 4 shows the installation ofthe ILT 40 to the lower open end 38 of the lower part of the pipeline20, to form a re-join or re-continuation of the pipeline 20.

In an alternative operation (not shown), the ILT 40 is first installedfor example by welding to the lower open end 38 of the lower part of thepipeline 20. After welding, the ILT 40 can be filled with water from itsopen top end. A small air gap may be left in order to weld the ILT 40 tothe upper end 36 of the pipeline 20 to absence the presence of waterduring the welding.

The ILT 40 has a typically ‘T-port’ 43, and also includes a vent port42. The vent port 42 may be an already integral part of the ILT 40, or adedicated port added to the ILT 40 for the present invention. The ventport 42 could comprise a relatively angled pipe including a ‘stuffingbox’ arrangement, having fill and drain ports, etc. The ‘stuffing box’arrangement allows the sealed passage of a vent hose 46 therethrough.

The vent hose 46 is extended through the stuffing box to have aninternal part 46 b ending at one end 48 at or near the highest internalpart of the pipeline 20, and an external part 46 a. The vent hose 46could be pushed into or pulled out of the pipeline 20 via one or more(hydraulic or electric) cable pushers (not shown). An indicator or markon the vent hose 46 could also indicate when the end of the vent hose 46has reached the required high point of the pipeline 20.

The vent hose 46 may be made from rubber or polymer hose, and can bere-enforced with steel armour wires in order to work with the requiredpressures. The vent hose 46 internal diameter may be in the range 10 mmto 100 mm, and the wall thickness in the range 2 to 5 mm. The vent hose46 can be stored on a reel prior to entering the pipeline 20. Forexample, the vent hose 46 could be made of an HDPE inner tube,overwrapped with fiberglass for strength and wear resistance. Such adesign is flexible enough to manoeuvre into the pipeline 20, but rigidenough to be pushed up to the highest point.

The vent hose 46 could also have a simple stainless steel fitting on theend to help guide it along the pipeline 20 without damaging the pipelineliner.

New flooding fluid 32 a can then be added into the drained portion 34,either by addition to the still fluid-filled oblique part 24 of thepipeline 20 (via a suitable access point or port, generally being at ornear the reel, to spill over into the drained portion 3 as per arrow G),or through the ILT 40 as per arrow F, whilst the air trapped in thedrained portion 34 can be vented through the end and internal andexternal parts of the vent hose 48, 46, 46 a, to atmosphere, until thenew flooding fluid 32 a reaches the vent hose end 48, and will bevisible by now pouring out of the end of the external part of the venthose 46 a.

After the re-filling, the internal part 46 b of the vent hose can bewholly or substantially withdrawn through the stuffing box in the ventport 42, until the end 48 is withdrawn, or at least located in the ventport 42, followed by sealing of the vent port 42 in a manner known inthe art.

In this way, the previously drained portion 34 and the ILT 40 are nowwholly or substantially filled with flooding fluid (now all labelled32), as shown in FIG. 6. Optionally, the flooding fluid 32 can bepressurised by a pump or the like at or near the reel and through asuitable access port as previously discussed. The pipeline 20 is nowready to continue to be reel-layed through the moonpool 28 as shown inFIG. 6.

In a second particular embodiment of the present invention, a second cutof the pipeline 20 is made to remove a section of the pipeline 20,leaving upper and lower open ends of the pipeline, one or which may bethe same as upper and lower open ends 36, 38 described herein, to createthe space required to fit the longer In-Line Structure (ILS) between thelower open end 38 and a new upper end (not shown) of the pipeline 20.The ILS then re-joins or continues the pipeline 20 as a single pipelineto enable the method of the present invention and for further laying.

In a third particular embodiment of the present invention, a second cutof the pipeline 20 is made to remove a section of the pipeline 20,leaving upper and lower open ends of the pipeline, one or which may bethe same as upper and lower open ends 36, 38 described herein. An endILS or a terminal ILS, such as a PLET, may be added to each of the upperand lower open ends to provide separate pipelines for different layingoperations.

For example, FIG. 7 shows the addition of a first PLET 58 to the openend 62 of the lower part 33 of the pipeline 20, so that the lower part33 can then be continued to be laid from the vessel 30 into the sea 8.Either before or after such action, a second PLET 60 is added to theopen end 64 of the upper part 80 of the pipeline 20.

With the installation of the second PLET 60, the operator can proceedwith reflooding of the drained portion 34 of the upper pipeline part 80in accordance with a method of the present invention as describedherein, such as the embodiment described hereinabove and based on venthose 46 passing through a vent port 66 in the second PLET 60, so thatthe upper pipeline part 80 of the pipeline 20 on the reel 4 is refloodedwith flooding fluid 32 as shown in FIG. 8, and is ready to safely passover the aligner 22 and continue to be reel-layed through the moonpool28, etc., or the vessel 8 may relocate for reel-laying the remainingpipeline in another location.

FIG. 8 also shows a development of the vent port 66, which could includea T-valve 68 and incorporate a full bore flange 70, so that once thepipeline 20 is reflooded and the vent hose 46 removed, the full boreflange 70 can be closed. A stuffing box or similar could be mounted ontothe full bore flange 70, and can be removed once reflooding is achieved,and replaced with a blind flange 72 to provide a second barrier againstany leakage.

The present invention provides a method of installing an In-LineStructure (ILS) into a fluid-filled pipeline extending from a reel andover an aligner during offshore reeling, by providing fluid back intothe pipeline around the aligner to allow its movement for theinstallation of the ILS between cut ends. In this way, complete drainageof the entire pipeline is avoided, or at least within the drainage ofthe pipeline remaining on the reel, whilst allowing movement of the cutpipeline during the installation process.

It can be seen by the discussion herein above and the Figures that theoperator has a number of options available, including but not limitedto:

-   -   one or two cuts of the pipeline to create lower and upper open        ends;    -   using one or two ILSs; and    -   refilling flooding fluid from different entry ports;

and that the operator can use many combinations of these options toachieve different ILS installation and laying alternatives, and all suchcombinations are within the scope of the present invention.

1. A method of installing an In-Line Structure (ILS) to a fluid-filled pipeline extending from a reel, over an aligner, and through a lay-tower during offshore reeling, the pipeline having an oblique part from the reel to the aligner, and a vertical part from the aligner through the lay-tower, comprising at least the steps of: (a) draining fluid in the fluid-filled pipeline from the vertical part of the pipeline to create a drained portion of the vertical part of the pipeline up to and around the aligner; (b) cutting the pipeline at or near the draining of step (a) to create upper and lower open ends of the pipeline; (c) installing the In-Line Structure to at least the upper open end of the pipeline; (d) locating a vent hose through a vent port in the In-Line Structure; (e) adding fluid into the drained portion of the pipeline and venting air from the drained portion of the pipeline through the vent hose to wholly or substantially fill the drained portion of the pipeline with the fluid.
 2. The method as claimed in claim 1, comprising installing the In-Line Structure (ILS) between the upper and the lower open ends of the pipeline.
 3. The method as claimed in claim 1, further comprising the step of installing a second In-Line Structure (ILS) to the lower open end of the pipeline.
 4. The method as claimed in claim 1, wherein the fluid in the fluid-filled pipeline is pressurised, and further comprising the step of relieving the pressure of the fluid prior to step (a).
 5. The method as claimed in claim 1, wherein the fluid in the fluid-filled pipeline is re-pressurised after step (e).
 6. The method as claimed in claim 1, further comprising forming a hole in the vertical part of the pipeline to allow the draining of the fluid from the vertical part of the pipeline.
 7. The method as claimed in claim 1, further comprising wholly or substantially removing the vent hose from the pipeline after step (e) and sealing the vent port in the In-Line Structure.
 8. method as claimed in claim 1, further comprising adding the fluid in step (e) into the In-Line Structure.
 9. The method as claimed in claim 1, further comprising adding the fluid in step (e) into the fluid-filled oblique part of the pipeline.
 10. The method as claimed in claim 1, further comprising moving the oblique part of the pipeline between step (b) and step (c).
 11. The method as claimed in claim 1, further comprising cutting the pipeline to remove a portion of the pipeline greater than the length of the In-Line Structure.
 12. An apparatus for installing an In-Line Structure (ILS) to a fluid-filled pipeline, extendable from a reel, over an aligner, and through a lay-tower during offshore reeling, the pipeline having an oblique part from the reel to the aligner, and a vertical part from the aligner through the lay-tower the apparatus comprising: (a) a drain to drain fluid from the vertical part of the pipeline to create a drained portion of the vertical part of the pipeline up to and around the aligner; (b) a cutter to cut the pipeline at or near the draining of step (a) to create upper and lower open ends of the pipeline; (c) an In-Line Structure having a vent port to install to at least the upper open end of the pipeline; (d) a vent hose to be installed in the vent port of the In-Line Structure; (e) fluid to wholly or substantially fill the drained portion of the pipeline; (f) a seal to seal the vent port after step (e). 